<header class="header_form">
    <h1>Nouvelle catégorie</h1>
</header>

<form class="ajax_form" action="./" method="post">
    <input type="hidden" name="todo" value="gestion[newCategorie]" />
    <p>
        <label>Nom</label>
        <input type="text" name="name" size="35" required />
    </p>
    <p id="bouton">
        <button type="submit">Valider</button>
    </p>
</form>